Bypass Screen Lock When Switching Users

[Z3ro3X]

I'm running Gnome Shell on Ubuntu 12.10. My screen was locked and my sister logged on her account. When she logged off her account it instantly switched to my account completely unlocked with out the need of typing my password. I tested it several times to see if it was a one time glitch. I was able to reproduce the error by first logging on my account, locking it, on the unlock screen I clicked on sign on to other user (forgot to mention, I'm using GDM instead of LightDM) and logged on my sister's account. I locked hers and logged back on mine. I than locked my again and logged back on hers. I than logged completely off her account and it instantly logged on mine bypassing the lock on my account.

I wouldn't know where to begin on how to fix this. But it's definitely a security problem.

Update: I just rebooted my system and I tried again to reproduce this and was unable to do so. So what ever the glitch is it seems to be gone now.